We are planning to continue correlated biochemical and ultrastructural studies on the ischemic brain of the gerbil. We have found during the past year that disaggregation of neuronal polyribosomes occurs in intact gerbils during the ischemic phase and continues for some time after restoration of cerebral circulation. We have begun a study using radioactive leucine, designed to provide information on the step or steps in the protein synthetic mechanism of neurons that are interfered with in ischemia. This study we plan to continue. Continuation of collaborative studies on the ultrastructure of cerebral tissue from lead-poisoned rats and monkeys is also planned. Continued work on the ultrastructure of unfixed, fresh-frozen sections of cerebral cortex is proposed with particular reference to enhancing visibility of membranes systems without exposing the tissue to solvents of any kind during preparation.